How do I open the yellow eco vent in snowy mountain and on the mountain..

Go to the fort. Follow the river till you see the frozen waterfall, there is a group of trees near the bottom of the water fall, go through them. Follow the path, collect the Power Cell and press the button!

It's up on Snowy Mnt.

The last secret power cell in the red sages lab is in a blue box up in the rock pillars near the spider cave. You have to get some yellow eco from the spider cave then drop down and run back towards the red sages lab before the eco runs out. It takes a couple tries to get there and shoot the box before your eco runs out but that's where the challenge is. I find that roll jumping gets me through the cave quicker. Hope this helps.

Stand in front of the fort in Snow Mountain and face the gates, turn right and follow the frozen river. When you reach the end of the river, there should be a little area full of snow and a small bunch of trees bunched together to the right, run through the trees and complete the little passage way full of obstacles and such. Once you've completed it, there should be a power cell in the room that you've probably entered. Go up onto the platform and grab the power cell, and that should automatically press the button that activates the yellow eco.